Do we need seat belts with Heat Pumps?
| Chaz Andrews, Technical Manager at Doepke UK, asks, “Should we follow safety recommendations made in product standards?” |
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I am old enough to remember traveling in cars without seatbelts. Yes – people did argue that seatbelts did not make cars safer and they were an unnecessary additional cost! So, what is the problem with clear, simple, and safe guidance being given to the UK electrical industry on the “Type” and use of RCDs with Heat Pumps (HP)? The Heat Pump Association published its guidance in March 2025. The 1st recommendation (see Q&A 6) highlights the requirements of BS7671 134.1.1 / 510.3, i.e., to follow manufacturers' recommendations. That is, if the HP manufacturer recommends the use of RCDs with their equipment, you are ill-advised to go against their recommendations, because that is what the HP safety standard is advising as well. So, does that mean that if the HP manufacturer's documentation does not make specific recommendations about RCDs, you can do what you like? No – BS7671 531.3.3 specifically states RCDs must be selected considering the presence of DC components and frequencies. We are aware that some manufacturers' installation instructions may contain issues, either due to ignorance, a genuine error, deliberate omission, or unclear instructions, which could be used to gain a commercial advantage, such as failing to highlight the requirement to use Type B RCDs. Considering the current market knowledge, we must request that HP manufacturers clarify the RCD requirements for their equipment. RCD Type vis-à-vis HP efficiency As we explained in 2022, *reference to technical article 23, Inverter (semiconductor control system) controlled equipment, permanently connected to the supply, requires either the manufacturer of the equipment to specify the Type of RCD clearly in their installation instructions or the installer has no option but to use Type B**. In a nutshell, lower-efficiency HPs, which do not use inverters, may be suitable for use with Type A RCDs (refer to the manufacturer's installation instructions). However, it should be noted that transients associated with compressor capacitive starting characteristics could result in unwanted RCD tripping during switch-on. Be highly cautious of claims that equipment is suitable for use with Type A RCDs, as it may lead to future problems on-site. Higher efficiency HPs utilise semiconductor control systems to provide soft start feature, i.e., reduced voltage starting, for compressors. Additionally, the semiconductor control system enables the speed of the compressor and fan to be adjusted based on heating and cooling demands. The characteristics of the control system determine the Type of RCD – see below. Annex H of BS ENIEC 62477 provides valuable guidance on the suitability and selection of RCDs for use with semiconductor control systems (PECS for short). Whilst this standard is primarily for technical committees producing product standards, Annex H provides a means of reaching reasoned and structured decisions relating to RCD selection associated with HPs. It gives examples of basic circuit diagrams, associated fault currents, and the appropriate Type of RCD: Type F RCDs are designed for use with single-phase supplied inverters, having very specific characteristics – *reference to technical article 23: For example, Type F can be used with inverter switching frequencies up to 1 kHz, provided the smooth DC content does not exceed specified values. To achieve improved efficiency performance, HP manufacturers are now employing inverters with switching frequencies above 1 kHz, which are outside of the performance range of Type F and some manufacturers' Type B RCDs –* reference to technical article 34. |
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To simplify selection owing to the limits of the current BSEN Type B product standard and issues with Type B RCDs that only work effectively < 1 kHz, Doepke introduced the Type B HP RCD in 2023, clearly indicating its suitability for use with HPs. Other manufacturers are now replicating this. High demand has led to a decrease in manufacturing costs and market prices. Installing HPs with increased efficiency performance (modern inverter control) that requires the use of Type B RCD, as opposed to lower-performance HPs associated with Type A RCDs, is a no-brainer when considering the total lifetime running cost for the homeowner. RCD or not to RCD? Standards Committees have a duty of care to the users of the standards and those who may be harmed through the associated designs and practices. Standards reflect best practice at the time the standard is written. Consequently, there is always inertia within the market to adopt new installation practices to support new product technology. Companies applying standards in product design or installation practice, must decide whether to prioritise safety implications (such as death or injury to a person) over the cost of the safety feature. Note; The Sentencing Council specifically lists "cost-cutting at the expense of safety" as a factor that can be used to increase the severity of a sentence. The latest safety standard covering domestic ASHPs (BSENIEC 60335-2-40:2024) states in short “installation instructions for appliances intended to be permanently connected to fixed wiring, having a leakage current < 10 mA, shall state that the installation of a residual current device (RCD) not exceeding 30 mA is advisable.” The term shall, in a standard, indicates a mandatory requirement, i.e., you must do it to meet the standard. The term advisable (all standards are advisory) is taken as reasonable or proper under the circumstances. Consequently, ASHP manufacturers who do not include the above requirement in their documentation do not meet the ASHP product standard. BS7671 clause 134.1.1 states that “the installation of electrical equipment shall take account of manufacturers’ instructions”. See BS 7671 clause 642 as well. The IET is unlikely to issue guidance that contradicts a published safety standard and or manufacturers’ instructions, unless a specific safety issue has been identified. Does an RCD add significantly to the lifetime costs of HP Installation? Generally, when we think of domestic fixed equipment, it is typically mounted inside a clean, well-organised environment. Externally ground-mounted chunks of metal connected to a 240V supply are a relatively new consideration for the UK – less than 1% of properties have HPs to date. Ultimately, under UK law, the responsibility lies with the HP Manufacturer, the company or person responsible for specifying the electrical installation, and those who sign the installation certificate. We cannot argue that an RCD significantly adds to the lifetime costs of HP installations, particularly when choosing high-efficiency HPs with solid-state control. *Technical Article 23 -Heat Pump RCDs Type F or B, Technical Article 20 -Type F RCDs, Technical Article 34 - HP Type B RCDs Featured in the Industry Press! The above article has been featured in several leading magazines: Electrical Times (July Edition, p. 50) Electrical Contracting News (August Edition) Professional Electrician (Sept Edition) Professional Electricians Wholesaler (Sept Edition) |